1. Field of the Invention
This invention is related to wrench-type tools, and specifically to wrenches adapted to fit locknuts such as those used on electrical conduit.
2. Description of the Related Art
Locknuts are designed to secure themselves to the surface against which they are tightened; this surface is referred to herein as a "contact surface." Locknuts come in a wide variety of shapes and sizes, and have a number of applications. One widespread use of locknuts is in assembling electrical conduit, especially to join sections of conduit to junction boxes and fittings, and to attach fittings such as wire clamps to junction boxes. Many millions of these locknuts are used annually in the United States. Locknuts for electrical conduit are referred to herein as "electrical locknuts" or simply "locknuts."
Locknuts for electrical conduit are typically annular pieces of soft metal with threads on an inner surface of the ring and with lugs or ears projecting from the perimeter of the ring. The lugs, usually six or eight in number, are twisted slightly relative to the main part of the ring; the twist improves the grip of the lugs against a contact surface such as an electrical junction box. Also, the entire locknut usually has slightly concave shape; the concave side is placed against a surface, again to increase the purchase of the locknut.
Tightening and removing locknuts is generally accomplished by placing the blade of a screwdriver against a lug of the locknut, and rapping on the handle of the screwdriver with hammer, pliers, or some other tool. This method often results in skinned knuckles and damaged tools, while a slipped screwdriver may contact a live circuit and result in possible electrocution or fire. Hence the need for a safe and efficient wrench for tightening and loosening locknuts.
Several tools for locknuts have been patented. Barnes discloses a spanner type drive head similar to a mechanic's socket wrench, with teeth to engage a locknut. Bowles, Vibber, and Young disclose wrenches having a member to fit inside an opening in the conduit and another member or members to engage a locknut. Houghton discloses another socket-type wrench with teeth to engage locknut lugs. Gagne discloses an open-end wrench with two teeth on its head. Hockenberry discloses a spanner wrench with a semi-cylindrical base having notches to fit around the lugs on a locknut. Apparently only the Gagne and Hockenberry tools can be fitted around a piece of conduit and onto a locknut on the conduit; i.e., to a locknut which is not at the end of a section of conduit.
U.S. patents of which Applicant is aware, including those mentioned in the preceding paragraph, are listed below:
______________________________________ U.S. Pat. No. Issue Date Patentee ______________________________________ 1,633,297 Jun. 21, 1927 Vibber 1,752,074 March 25, 1930 Gagne 2,233,046 Feb. 25, 1941 Bowles 2,522,038 Sep. 12, 1950 Houghton 2,575,779 Nov. 20, 1951 Young 3,768,345 Oct. 30, 1973 Barnes 4,848,195 Jul. 18, 1989 Hockenberry ______________________________________